generate schemastore for flox manifest

[ghudgins]

Problem

When I am using an IDE I need my IDE to automatically suggest Flox's schema So I can more easily work with the manifest in my IDE

Acceptance Criteria

• generate a JSON schema for the manifest.toml
• contribute the schema to https://www.schemastore.org/ via https://github.com/schemastore/schemastore/
• create a test that is explicit about schema changes needing to get contributed to https://github.com/schemastore/schemastore/